Raimixer

- Much improved GUI (`raimixer --gui`); now it doesn't lacks any option that the command line version do.
- Option to left the additional amounts in mixing accounts (that won't be deleted) to help obfuscate future mixing sessions.
- Mixings can be cancelled before they finish.
- `--clean` renamed to `--consolidate`.
- `--delete_empty` to delete empty accounts (also in the GUI as a checkbox) after consolidating.
- Option to send from many mixing accounts to the destination.
- Fixes.

- Lots of usability fixes: default account and wallet are now read from the RailBlock's config file so the user
doesn't have to specify them, reworked options and help, clean output, etc.

- Python package published on Pypi.

- Improved the readme.

- Added some tests.

- First release.